[GHC] #9805: Use TrieMaps to speed up type class instance lookup

[GHC]

#9805: Use TrieMaps to speed up type class instance lookup
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        Reporter:  ezyang            |                Owner:  ezyang
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.9
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 There shouldn't be a map for `CastTy` in the trie. See `Note [Non-trivial
 definitional equality]` in !TyCoRep. Remember that `ty |> co` is equal to
 `ty` if the kinds are the same. A more interesting scenario: `(t1 |> co1)
 (t2 |> co2)` is equal to `t1 t2` if the kinds are the same. Note that it
 might be that neither `co1` nor `co2` is reflexive!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9805#comment:17>
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